Methods and apparatus for controlled-angle wafer immersion

ABSTRACT

The orientation of a wafer with respect to the surface of an electrolyte is controlled during an electroplating process. The wafer is delivered to an electrolyte bath along a trajectory normal to the surface of the electrolyte. Along this trajectory, the wafer is angled before entry into the electrolyte for angled immersion. A wafer can be plated in an angled orientation or not, depending on what is optimal for a given situation. Also, in some designs, the wafer&#39;s orientation can be adjusted actively during immersion or during electroplating, providing flexibility in various electroplating scenarios.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to the following US Patent Applications:U.S. patent application Ser. No. 09/927,741 naming Jonathan Reid, StevenMayer, Marshall Stowell, and Evan Patton as inventors, titled “ImprovedClamshell Apparatus for Electrochemically Treating Wafers,” and filed onthe same day as the present invention now pending; U.S. patentapplication Ser. No. 09/872,340 naming Evan Patton, David Smith,Jonathan Reid, and Steven Mayer as inventors, titled “Methods andApparatus for Bubble Removal in Wafer Wet Processing,” and filed on thesame day as the present invention now pending; and U.S. patentapplication Ser. No. 09/927,740 naming Steven Mayer, Marshall Stowell,Evan Patton, and Seshasayee Varadarajan as inventors, titled “Methodsand Apparatus for Controlling Electrolyte Flow for Uniform Plating,” andfiled on the same day as the present invention now pending. Each ofthese applications is incorporated herein by reference for all purposes.

FIELD OF THE INVENTION

This invention relates to electroplating technology, such as waferelectroplating. Even more specifically, the invention pertains tomethods and apparatus for controlled-angle wafer handling for thepurpose of improving electroplated wafer uniformity, quality, andthroughput.

BACKGROUND OF THE INVENTION

Electroplating has many applications. One very important developingapplication is in plating copper onto semiconductor wafers to formconductive copper lines for “wiring” individual devices of theintegrated circuit. Often this electroplating process serves as a stepin the damascene fabrication procedure.

A continuing issue in modern VLSI wafer electroplate processing isquality of the deposited metal film. Given that metal line widths reachinto the deep sub-micron range and given that the damascene trenchesoften have very high aspect ratios, electroplated films must beexceedingly homogeneous (chemically and physically). They must haveuniform thickness over the face of a wafer and must have consistentquality across numerous batches.

Some wafer processing apparatuses are designed to provide the necessaryuniformity. One example is the clamshell apparatus available in theSABRE™ electroplating tool from Novellus Systems, Inc. of San Jose,Calif. and described in U.S. Pat. Nos. 6,156,167, 6,159,354 and6,139,712, which are herein incorporated by reference in their entirety.The clamshell apparatus provides many advantages in addition to highwafer throughput and uniformity; such as wafer back-side protection fromcontamination during electroplating, wafer rotation during theelectroplating process, and a relatively small footprint for waferdelivery to the electroplating bath (vertical immersion path).

There are many factors that can effect the quality of an electroplatingprocess. Of particular note in the context of the present invention areproblems having their genesis in the process of immersing the wafer intoan electroplating bath. As indicated, bubbles can be entrapped on theplating underside of the wafer (the active side) upon immersion. This isespecially true when the wafer is immersed in a horizontal orientation(parallel to a plane defined by the surface of the electrolyte) along avertical immersion trajectory. Depicted in FIG. 1A is a cross-sectionaldiagram of a typical bubble-entrapment scenario arising in anelectroplating system 101. A horizontally oriented wafer 103 is loweredtowards an electrolyte 107 in a vessel 105 along a vertical Z-axis andultimately immersed in the electrolyte. Vertical immersion ofhorizontally oriented wafer 103 results in air bubbles 109 being trappedon the underside (plating surface) of wafer 103.

Air bubbles trapped on the plating surface of a wafer can cause manyproblems. Bubbles shield a region of the plating surface of a wafer fromexposure to electrolyte, and thus produce a region where plating doesnot occur. The resulting plating defect can manifest itself as a regionof no plating or of reduced thickness, depending on the time at whichthe bubble became entrapped on the wafer and the length of time that itstayed entrapped there. In an inverted (face down) configuration,buoyancy forces tend to pull bubbles upwards and onto the wafer's activesurface. They are difficult to remove from the wafer surface because theplating cell has no intrinsic mechanism for driving the bubbles aroundthe wafer edges, the only path off the wafer surface. Typically, wafer103 is rotated about an axis that passes through its center and isperpendicular to its plating surface. This also helps to dislodgebubbles through centrifugal force, but many of the smaller bubbles aretenacious in their attachment to the wafer.

Therefore, while horizontal wafer orientation (especially coupled with avertical immersion trajectory) has numerous advantages from a hardwareconfiguration and throughput standpoint, it leads to technicallychallenging issues associated with gas entrapment and consequent defectformation.

One way to facilitate removal of entrapped bubbles is to use avertically directed electrolyte flow aimed at the plating surface of thewafer. This can help dislodge the bubbles. As depicted in FIG. 1B,scenario 102, plating solution is directed from a conduit 111 normal tothe plating surface of the wafer at a velocity sufficient to dislodgeentrapped bubbles. As indicated by the arrows emanating from 111, themajority of the flow is directed at the center of wafer 103. As the flowencounters the surface of the wafer, it is deflected across the wafersurface to push the bubbles toward the sides of wafer 103 as indicatedby the dashed arrows. This helps remove bubbles that are not onlygenerated upon immersion, but also those formed or reaching the surfaceduring electroplating. Unfortunately, the radial non-uniformity of theforced convection of such systems can result in non-uniform platingprofiles. This is because the electroplating rate is a function of localfluid velocity, and the forced convection of the systems such asdepicted in FIG. 2B introduces non-uniform velocity profiles across thewafer surface.

Another problem associated with vertical immersion of a horizontallyoriented wafer is multiple wetting fronts. When a wafer is immersed inthis way, the electrolyte contacts the wafer at more than one point,creating multiple wetting fronts as the wafer is submerged in theelectrolyte. Where individual wetting fronts converge, bubbles may betrapped. Also, defects in the finished plating layer can be propagatedfrom microscopic unwetted regions formed along convergence lines ofmultiple wetting fronts.

What is needed therefore is a way to improve plated metal quality.Improved methods and apparatus should reduce the problems that can arisefrom bubble formation and multiple wetting fronts during waferimmersion.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for controlling theorientation of a wafer with respect to the surface of an electrolyteduring an electroplating process. A wafer is delivered to an electrolytebath along a trajectory normal to the surface of the electrolyte. Alongthis trajectory, the wafer is angled before entry into the electrolytefor angled immersion. A wafer can be plated in an angled orientation ornot, depending on what is optimal for a given situation. Also, in somedesigns, the wafer's orientation can be adjusted actively duringimmersion or during electroplating. Active angle adjustment refers tochanging the angle of the wafer at any time during positioning orplating. This provides flexibility in various plating scenarios.

Stated somewhat differently, the invention provides methods andapparatus for wafer movement that embody two movements: first, movingthe wafer into and out of a plating bath along a trajectorysubstantially normal to the surface of the electrolyte; and second,adjusting the angle of the wafer with respect to the surface of theelectrolyte. These discrete movement functions are performed eitherconcurrently or separately. Apparatus for performing the two movementshave two actuators, one for each movement; therefore the movements canbe separately controlled depending on the electroplating processdemands. In one example, a wafer is tilted as it is immersed in aplating bath; in another example the wafer is tilted and then directedinto the plating bath. In yet another example, the wafer is tilted to anew angular orientation after it is immersed in the bath at a firstangular orientation.

One aspect of this invention pertains to methods of positioning a waferduring electroplating. In one preferred embodiment, a wafer is loadedand/or unloaded from an electroplating apparatus in a horizontalorientation relative to the surface of the plating bath. Duringelectroplating, the angle of the wafer is actively changed toorientations that are optimal for reasons particular to eachelectroplating event. The wafer is rotated or not, depending on thedesired characteristics of the plated metal film.

Of particular importance to the quality of the deposited metal film on awafer with respect to the methods of the invention are four factors: (1)the linear speed at which the wafer is immersed and withdrawn from anelectroplating bath, (2) the rotational speed of the wafer, (3) theangle of the wafer surface with respect to the electrolyte surface, and(4) the “swing speed” or angular speed upon tilting of the wafer. All ofthese factors (and combinations thereof) have important ramifications tothe quality of the deposited metal film resulting from methods herein,as will be discussed below.

Methods of the invention utilize wafer immersion into an electrolytealong a vertical trajectory; that is, along an axis substantially normalto the electrolyte surface. Of particular importance is the speed atwhich this immersion (or extraction) of the wafer is performed. If thespeed is too fast, then the plating process and ultimately the depositedfilm quality will suffer. If the speed is too slow, then throughputsuffers. Preferably the speed for immersion and extraction of a wafer isbetween about 5 and 50 millimeters/second.

Rotation speed of a wafer is important for a number of reasons. Ofparticular importance is the speed of rotation during immersion andplating. If the wafer is rotated too quickly during immersion, frothingof the electrolyte can form bubbles that become entrapped on the wafersurface causing defects in the plated metal film. If the wafer isrotated too slowly, then film homogeneity may suffer. Preferably therotational speed for immersion and extraction of a wafer is betweenabout 50 and 150 rpm, depending on the wafer diameter. Larger diameterwafers are generally rotated more slowly than smaller diameter wafers.

The tilt angle of the wafer is important as a means to allow bubbles toescape that otherwise would become entrapped on the wafer surface.Angled immersion is important also with respect to wetting fronts formedupon immersion of the wafer into a plating bath. The preferred angle forthis invention has been found to be about 5 degrees or less fromhorizontal.

The swing speed or angular speed upon tilting of the wafer is importantfor example when a wafer is already immersed in a plating solution andthe tilt angle is changed. If the angle is changed too quickly, theplating solution may be splashed or agitated to a state of frothing.Again, this causes bubbles which are detrimental to the plating processand are to be avoided. Preferably, the swing speed is between about 0.25and 3 degrees per second.

As mentioned, the invention finds particular use in the context ofcopper electroplating. In modem damascene processing, conditions have tobe increasingly stringent for optimal plating quality and throughput.The invention provides plating environments with less possibility fordefects caused by bubbles and multiple wetting fronts.

Another aspect of this invention pertains to apparatus for implementingthe method of the invention. Apparatuses of the invention include onecomponent that can tilt the wafer with respect to the surface of theelectrolyte during vertical positioning in the electroplating processand another component that can translate the wafer vertically into andout of the electrolyte. This allows a wafer holder component to betilted as well as lifted in and out of the electrolyte bath, usingseparate actuators for each movement component. In a preferredembodiment, one component of the apparatus has an “inverted pendulum”configuration that allows such tilting. In this embodiment, a waferholder component is tilted by moving its distal end (the end away fromthe wafer) along an arced track with movement provided by a firstactuator. The proximal end of the wafer holder provides a fixed pivotpoint at or near the wafer. The wafer holder, arced track, and firstactuator form an assembly that is moved along a vertical trajectorydriven by a second actuator, which provides substantially linearbi-directional movement of the wafer into or out of an electrolyte bath.

These and other features and advantages of the present invention will bedescribed in more detail below with reference to the associated figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description can be more fully understood whenconsidered in conjunction with the drawings in which:

FIG. 1A is a cross-sectional diagram of a typical bubble-entrapmentscenario.

FIG. 1B is a cross-sectional diagram of a bubble removal scenarioemploying axially-directed electrolyte flow.

FIG 1C is a cross-sectional diagram of a wafer having a verticalorientation (normal to a plane defined by the surface of an electrolyte)along a vertical immersion path (z-axis).

FIG. 2A is a detailed flowchart of a preferred embodiment of the methodof electroplating a wafer with active angle positioning.

FIGS. 2B-2I are schematic illustrations of an electroplating cell andwafer at various stages in the process depicted in FIG. 2A.

FIG. 3A is a simplified block diagram of a front view of a waferpositioning apparatus of the invention.

FIG. 3B is a simplified block diagram of a side view of a waferpositioning apparatus of the invention.

FIGS. 3C-E are block diagrams as in FIG. 3A and depicting movement ofthe wafer positioning apparatus.

FIG. 4A depicts an apparatus of this invention for electrochemicallytreating semiconductor wafers.

FIGS. 4B-C depict components of the apparatus shown in FIG. 4A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description of the present invention, a fewspecific embodiments are set forth in order to provide a thoroughunderstanding of the invention. However, as will be apparent to thoseskilled in the art, the present invention may be practiced without thesespecific details or by using alternate elements or processes. In somedescriptions herein, well-known processes, procedures, and componentshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

A central aspect of the invention pertains to methods of positioning awafer relative to a plane defined by the surface of an electrolyte in anelectroplating apparatus. Generally, the positioning involves twooperations: (1) moving the wafer into or out of the electrolyte along atrajectory substantially normal to the plane defined by the surface ofthe electrolyte, and (2) adjusting the angle defined by the relativeposition of a planar plating surface of the wafer with respect to theplane. See FIGS. 3D and 3E, for example. In many embodiments, the angleadjustment takes place while the wafer's angular pivot point is itselfstationary or moving linearly along the trajectory normal to the planedefined by the surface of the electrolyte. This positioning methodprovides angle control during immersion and plating, if necessary. Themovements of translating the wafer vertically into or out of theelectrolyte and adjusting the angle of the wafer can be performed eitherconcurrently or in each in separate time frames.

In one specific embodiment, the immersion process is performed in aparticular sequence as set forth now and described in more detail belowwith respect to FIG. 2. This sequence involves first positioning thewafer horizontally, such that a planar plating surface of the wafer issubstantially parallel to a plane defined by the surface of theelectrolyte. In many designs, the wafer starts at a position above theelectroplating cell. Then the wafer is tilted at an angle such that theplanar plating surface of the wafer is no longer substantially parallelto the plane defined by the surface of the electrolyte. The tiltinggenerally takes place with the wafer positioned above the electrolyte.Either after the tilting or concurrently with the tilting, the wafer ismoved toward the electrolyte along a trajectory substantially normal tothe plane defined by the surface of the electrolyte. Finally, the waferis immersed in the electrolyte while the wafer is tilted.

In this method, the wafer's angular orientations may deviate from thehorizontal quite significantly (in the extreme example up to about 90degrees), as depicted in FIG. 1C. In scenario 104, any bubbles formedupon immersion of wafer 103 in electrolyte 107 will naturally rise alongthe face of the wafer and escape to the atmosphere. Thus, this verticalimmersion scenario is ideal for avoiding bubble entrapment and multiplewetting fronts. Preferably, however, the orientations deviate relativelylittle; e.g., by not more than about 20 degrees. In many embodiments ofinterest, the angular orientation deviates from the electrolyte plane byabout 5 degrees or less. In one specific embodiment, the wafer does notvary by more than between about 4 and 5 degrees from horizontal.

By using a relatively small angle of tilt, deviation from a smallerfootprint is lessened because components of apparatus designed toimplement the method need not project much beyond the area of theplating bath if at all. Plating baths need not be made any deeper orwider to accommodate apparatus designed to implement the method, andthus there is no need for additional expense for increased electrolytevolume.

Moving the wafer toward the electrolyte as described preferably occursat a speed between about 5 and 50 millimeters/second. More preferablymoving the wafer toward the electrolyte occurs at a speed between about5 and 25 millimeters/second. Even more preferably moving the wafertoward the electrolyte occurs at a speed between about 8 and 15millimeters/second. Most preferably moving the wafer toward theelectrolyte occurs at a speed of about 12 millimeters/second. The waferenters the electrolyte at these speeds, in an angled orientation. Thetilting operation may be accomplished while the wafer is moving at thesespeeds. Since the movement of the wafer into the electrolyte at theabove speeds takes place along a direction substantially normal to theplane of the electrolyte surface, the speed is sometimes referred to as“z-speed.” Note that the z-direction translation need not be absolutelyvertical or normal to the plane of the plane of the electrolyte. Givendesign tolerances and apparatus constraints, the trajectory may varyfrom the absolute normal by a slight amount; e.g., a few degrees. Theconcept of “substantially normal” encompasses the “absolute normal.”

Some or all of the operations described above may be performed while thewafer is rotating about an axis normal to the plating surface of thewafer. For many operations, the wafer is rotated at a speed of betweenabout 1 and 150 rpm. The rotational speed will vary depending upon theoperation. For electroplating, the wafer is preferably rotated at aspeed of between about 100 and 150 rpm when the wafer is about 200 mm indiameter. And, the wafer is preferably rotated at a speed between about50 and 100 rpm when the wafer is about 300 mm in diameter. Morepreferably, wafers of about 300 mm are rotated at a speed of about 90rpm. Other operations for which rotation may be appropriate includeimmersion (to facilitate wetting), spinning off excess electrolyte afterthe wafer is removed from the electrolyte cell, and rinsing the wafer.Each of these operations may have their own optimal range of rotationspeeds.

Also optionally, the method includes adjusting the angle of the wafer'splanar plating surface with respect to the plane defined by the surfaceof the electrolyte while the wafer is stationary with respect to adirection normal to the plane defined by the surface of the electrolyteor while the wafer is translating linearly in a trajectory normal tothat plane. In a particular embodiment, tilting is performed while thewafer is stationary with respect to the direction normal to the planedefined by the surface of the electrolyte. Adjustment may occur afterthe wafer is immersed in the electrolyte. In such cases, the waferassumes one angular orientation during immersion and a different angularorientation during plating. Using the methods and apparatus of thisinvention, one can control the angular orientation of the wafer atvarious stages of the actual plating operation.

As should be clear, the invention allows separate control of z-directiontranslation and angular tilting of the wafer. Preferably, though notnecessarily, the wafer is tilted during entry into the electrolyte. Theappropriate level of tilting for immersion may be accomplished atvarious points in the overall process. While the discussion abovegenerally assumes that the tilting occurs prior to z-directiontranslation, this need not be the case. In one embodiment, the wafer isfirst positioned horizontally above the electrolyte as described above.Then the wafer is moved toward the electrolyte along a trajectory normalto the plane defined by the surface of the electrolyte. At leastinitially in this process, the wafer is oriented horizontally. Next, thewafer is tilted at an angle such that the planar plating surface of thewafer is no longer substantially parallel to the plane defined by thesurface of the electrolyte. And finally, the wafer is immersed into theelectrolyte while the wafer is tilted.

As explained, angled immersion is important for avoiding entrapment ofbubbles on the plating surface formed during electroplating. And asexplained, methods can be performed with “active angle adjustment”; thatis, independent control of the angle of the wafer before, during, and/orafter immersion in the plating bath. At any one or more wafer positionsduring processing, the wafer may be tilted independently over a range ofangles. Preferably, such tilting is permitted while the wafer center (orits pivot point) is stationary in three-dimensional space or movingalong a defined trajectory during immersion into or removal from theelectroplating bath. Note that is not possible for wafers that arerigidly affixed to an arm that “swings” the wafer into a platingsolution.

In one embodiment of the aforementioned positioning method, the pivot isa “virtual” pivot. By “virtual” we mean that the wafer pivot point isnot defined by a hinge or other mechanical pivot mechanism. The pivotpoint is not at the location of a pivoting mechanical mechanism. Rather,the wafer pivots by virtue of separate mechanism located remote from thepivot point. Of course, the invention encompasses actual mechanicalpivots as well as virtual pivots. One example of a virtual pivot isprovided by a mechanism in which a wafer holder has an inverted pendulumdesign. In this design, movement of a part of the wafer holder locateddistally from the wafer actually causes the wafer to pivot upon an axispassing through a plane near and parallel to, or passing through thewafer. This will be explained in more detail below.

A more encompassing aspect of the invention pertains to methods ofelectroplating a wafer comprising positioning the wafer horizontally ata first height above an electrolyte, wherein a planar plating surface ofthe wafer faces and is parallel to a plane defined by the surface of theelectrolyte. Then the wafer is tilted at an angle such that the planarplating surface of the wafer is no longer parallel to the plane definedby the surface of the electrolyte. The wafer is then rotated along afirst axis normal to the planar plating surface of the wafer and whichpasses through the center of the wafer, at a first rotational speed.Next, the wafer is moved into the electrolyte along a trajectorysubstantially normal to the plane defined by the surface of theelectrolyte. Then the wafer is electroplated on its plating surface witha metal, and removed from the electrolyte along the trajectory to asecond height, below the first height, above the electrolyte.

In one embodiment, this method further comprises decreasing rotationrate from the first rotational speed to a second rotational speed priorto removing the wafer from the electrolyte.

In another embodiment, this method further comprises, after removing thewafer from the electrolyte, returning the wafer to horizontal, rotatingthe wafer at a third rotational speed, faster than the first rotationalspeed; in order to remove and reclaim a portion of the electrolyteremaining on the wafer. Then the wafer is raised to a third heightbetween the first and second height above the electrolyte. Finally thewafer is rinsed with a rinsing medium, spin-dried; and raised to thefirst height. In a specific embodiment, returning the wafer tohorizontal takes place at the second height.

As mentioned above, the following parameters may be important to theperformance of the plating process: the linear speed at which the waferis immersed and withdrawn from an electroplating bath, the rotationalspeed of the wafer, the angle of the wafer surface with respect to theelectrolyte surface, and the “swing speed” or angular speed upon tiltingof the wafer. The operations associated with these parameters may beperformed in various sequences. A specific example, method 201, ofelectroplating a wafer with active angle positioning will now bedescribed with reference to the flow chart of FIG. 2A and associatedschematic diagrams in FIGS. 2B-2I. Note that the invention may employany combination of the process operations depicted in FIGS. 2A-2I. Inmany embodiments, some fraction of the depicted process operations willnot be performed.

Method 201 is described with an electroplating apparatus in mind,although any wet wafer processing would apply wherein the wafer isimmersed into a bath of processing solution. Preferably copper iselectroplated onto the wafer. First, a wafer 240 is loaded into anelectroplating apparatus wafer holder (not shown), in a horizontalorientation at a first height 246. See 203. This orientation is commonlyemployed in wafer handling apparatus including robots for transferringwafers from one piece of apparatus to the next. The wafer can be loadedand unloaded from associated plating hardware in a horizontalorientation at the first height. The first height can vary, depending onthe hardware used to implement the method. Typically, the wafer'sinitial position (shown in FIG. 2B) is above the electrolyte such thatelectroplating takes place directly under this starting position.

Since many wafer processing tools require horizontal orientation ofwafers, this facilitates wafer throughput via integration with othertools; that is, wafers need not be reoriented before loading into a toolutilizing this method or before loading into another wafer processingtool after unloading from a tool utilizing this method. In the broadestsense however, the invention embodies methods and apparatus wherein thewafer's starting position is not horizontal (but rather as depicted inFIG. 2C). Also, handling a wafer along a vertical trajectory allowsassociated apparatus implementing the method to be designed with asmaller relative footprint than those requiring delivery of a wafer to aplating bath from positions not above the electrolyte.

Next the wafer 240 is tilted. See FIG. 2C and block 205 of FIG. 2A. Thisallows immersion of the wafer at an angle and thereby reduces theaforementioned wetting and bubble problems. Specifically, angledimmersion reduces the problems of bubble entrapment on the platingsurface and multiple wetting fronts. Depending on the electroplatingevent taking place and the details of the wafer holding apparatus(clamshell), optimally, different angles may be used. Note thatelectroplating at an angle helps prevent entrapment of bubbles on theplating surface during electroplating. Defects in the plated film arereduced when angled plating is employed. In operation 205, the angle ofthe wafer is preferably about 5 degrees or less. In a very specificembodiment, the angle is about 4.6 degrees.

Next the wafer is optionally rotated at a first rotational speed. SeeFIG. 2D and block 207 of FIG. 2A. As mentioned if wafer rotation andimmersion rate (z speed) is properly controlled, multiple wetting frontsand bubble formation (frothing) during immersion can be minimized. Asmentioned above, different rotational speeds may be employed fordifferent operations. For immersing the wafer, the rotational speed ispreferably between about 1 and 150 rpm. For a 200 mm diameter wafer, thespeed is preferably between about 100 and 150 rpm. For a 300 mm diameterwafer, the speed is preferably between about 50 and 100 rpm, morepreferably about 70 rpm.

The wafer is then immersed in the bath. See FIG. 2E and block 209 ofFIG. 2A. For the reasons described above, preferably the wafer is movedinto electrolyte 244 (in an electroplating cell 242) at a speed ofbetween about 5 and 50 millimeters/second. More preferably, at a speedof between about 5 and 25 millimeters/second. Even more preferably, at aspeed of between about 8 and 15 millimeters/second. Most preferably, ata speed of about 12 millimeters/second.

Next the process flow accounts for the options of plating horizontallyor at angled orientation. See 211. If the operation is to be conductedwhile tilted, then electroplating, preferably with copper, is done at aspecified angle. If not, then the wafer orientation is returned tohorizontal while in the electroplating cell 242. See FIG. 2F and block219 of FIG. 2A. This allows flexibility for plating environments that donot accommodate a tilted wafer for plating or in cases where horizontalplating is preferred. In this embodiment, the angular speed or “swingspeed” of the wafer may be important. Since the wafer is rotatingrelatively fast, if the wafer is tilted back to horizontal too quickly,then too much turbulence may result and create bubbles or splashing (andpossibly contamination of equipment with splashed electrolyte). As withall events in a high throughput environment, if the swing speed is tooslow, throughput suffers. Preferably, the swing speed of the wafer isbetween about 0.25 and 3 degrees per second. More preferably, the swingspeed is between about 0.25 and 1.5 degrees per second. Most preferably,the swing speed is between about 0.5 and 1 degrees per second. As well,any entrapped bubbles must be given time to escape while the wafer isstill tilted. Thus a delay is sometimes used before the wafer isreturned to a horizontal orientation. The delay time is preferablybetween about 1 and 20 seconds. More preferably the delay time is 2 to10 seconds. Most preferably the delay time is about 5 seconds. Once thewafer is oriented horizontally at 219, then it is plated in thatorientation. See FIG. 2F and block 221 of FIG. 2A.

Referring back to block 211, if the wafer is to be plated in a tiltedorientation, then the plating is conducted at 213. Once the wafer isfully electroplated, either in 211 or 213, its rotation is slowed fromthe first rotational speed to a second rotational speed (see 215) beforebeing extracted from the bath. It can be important to slow the rotationso that when the wafer is extracted from the bath, splashing and/orfrothing are minimized. It has been found that splashing or frothing canleave surface bubbles in the bath, which can become attached to thesubsequently plated wafer. Slowing rotation also minimizes vortexing. Ifa significant vortex is formed in the electrolyte from the rotationaldrag on the electrolyte surface during wafer extraction, then theresultant turbulence on the electrolyte surface can detrimentally effectwetting of the next wafer. Preferably, the second rotational speed isbetween about 25 and 75 rpm. More preferably, between about 10 and 50rpm.

After its rotation is slowed, the wafer is extracted from theelectrolyte. See FIG. 2G and block 217 of FIG. 2A. Also, in conjunctionwith slowing to a second rotational speed, the wafer extraction may bedone at a vertical linear speed (z-speed) that is the same as or lessthan that used for immersion. Preferably, extracting the wafer from theelectrolyte is performed at a speed between about 5 and 25millimeters/second. More preferably, extracting the wafer from theelectrolyte is performed at a speed of about 12 millimeters/second. Thewafer is elevated to a second height 248, below the first height, about30 millimeters above the electrolyte.

At this point, the process flow 201 (FIG. 2A) shows decision 223. If thewafer is not already horizontal, then it is returned to horizontal. See225. If the wafer is horizontal, then 225 is skipped. The next event isa reclaim. See FIG. 2H and block 227 of FIG. 2A. Still at the secondheight, the wafer's rotation is increased to a third rotational speed,faster than the first rotational speed, in order to remove and reclaim aportion of the electrolyte remaining on the wafer. Centrifugal forcethrows the electrolyte from the wafer and it is collected for reclaim ina receptacle (not shown). Preferably, the third rotational speed isbetween about 200 and 600. More preferably, the third rotational speedis about 400 rpm.

Next, the wafer is raised to a third height 250, between the first andsecond heights. See FIG. 2I and block 229 of FIG. 2A. This is done inorder to rinse any remaining electrolyte from the wafer surface.Ultra-pure deionized water or other appropriate cleaning fluid may beused to rinse the wafer, see 231. Preferably, rinsing the wafercomprises contacting the wafer with a steady stream of cleaning fluid252 near the center of the wafer at a flow rate of between about 100 and500 ml/minute for between about 1 and 2 seconds. Using a distinct, thirdheight allows reclaim of the rinse fluid in a separate reclaim apparatussince the rinse water (as does the electrolyte in its reclaim) sprays ina relatively tight band radially outward from the wafer, when the waferis rotating at the third rotational speed. Reclaim channels areeffective components of plating chambers to implement such a reclaimscenario. A good example of such a chamber is described in U.S. Pat. No.6,099,702 by Reid, et al, which is incorporated by reference herein.Preferably, the third height is about 100 millimeters above theelectrolyte. The wafer is then spin dried at the third height, see 233.Preferably, the spin dry is between about 1 and 2 seconds.

Finally, the wafer is returned to the first height and removed. See FIG.2B and block 235 of FIG. 2A. As described above, the wafer having beenreturned to its original starting point facilitates equipment designedto implement the method in coordinating with other wafer processingequipment, especially robot handlers, thus increasing throughput.

In one example, the second height is about 30 millimeters aboveelectrolyte 244 and the third height is about 100 millimeters above theelectrolyte. The first height (the starting or load location height) isabout 200 mm above the electrolyte. This invention also pertains toapparatus that facilitate angled immersion of the wafers intoelectroplating baths. Such apparatus should allow the flat activesurface of a wafer to assume multiple angles with respect to theelectrolyte surface. These angles represent deviations from thehorizontal wafer orientation in which its active surface is parallel tothe plane of the electrolyte surface. In other words, the apparatusshould allow the wafer to tilt about a pivot location on or near thewafer. Preferably, the apparatus accomplishes this without significantlyvarying the wafer's overall position in three-dimensional Cartesianspace. In other words, the apparatus should be able to tilt the wafer'sangle with respect to a plane parallel to the electrolyte's surface,without significantly translating the wafer. More specifically, somepoint or line on or near the wafer remains stationary during suchpivoting. For example, the wafer's pivot point or its center point mayremain fixed during pivoting.

Obviously, the apparatus should permit the full range of operationsassociated with electroplating. Thus, for example, the apparatus shouldpermit and/or drive movement of the wafer into and out of theelectrolyte bath. Preferably, though not necessarily, this isaccomplished via a linear trajectory—along a path substantially normalto the surface of the electrolyte. In addition, the apparatus shouldallow and/or drive rotation of the wafer about an axis through thecenter of its flat active surface. Parameters that may be controllablewith apparatus of this invention include the speed at which the wafer isrotated, the swing speed at which the wafer is tilted over a range ofangles, the total range of angles over which the wafer is tilted, thespeed at which the wafer is translated into and out of the electrolyte,and the like.

Apparatus suitable for use with this invention can take on manydifferent forms. It may include a variety of drive mechanisms, holders,pivot devices, and structural members. Generally, there will be a drivemechanism for controlling the rotation of the wafer. There may be one ormore other drive mechanisms that control tilting of the wafer andtranslation of the wafer. These drive mechanisms may be of manydifferent types such as hydraulic actuators, electric motors, screwdrives, and the like. Various wafer holders and tracks for moving thewafer holders may also be employed.

In one approach, wafer tilting is accomplished by an apparatus thatholds the wafer at a proximate end of a longitudinal member. Theapparatus maintains this end of the longitudinal member at asubstantially constant position in three-dimensional Cartesian space.The distal end of the longitudinal member is allowed to move over anarced path. This causes the wafer to tilt as described above. Asillustrated in FIGS. 3A-3D described below, the longitudinal member maytake the form of a wafer holder in an “inverted pendulum” orientation.

A simplified block diagram depicting a front view of a wafer positioningapparatus, 301, of this approach is depicted in FIG. 3A. Apparatus 301has a wafer holder 303. Wafer holder 303 has a proximal end that engagesa wafer 305, and a distal end movably connected to an arced track 311via an actuator 312. This arrangement is more easily visualized inconjunction with FIG. 3B, which depicts a block diagram of a side viewof wafer positioning apparatus 301. Wafer holder 303 is immovablycoupled to actuator 312. Also, wafer holder 303 rotates wafer 305 aboutan axis normal to the wafer planar plating surface 319. The componentsof 303 responsible for driving wafer rotation are not depicted. Theproximal end of wafer holder 303 is depicted as immersed in electrolyte309 of an electroplating cell 307 (anode components not depicted).

In this case, arced track 311 can be integral to plate 310 or attachedto plate 310. For example, arced track 311 can be a groove, channel, orrace formed in plate 310, a curved track or support along which actuator312 travels, or a curved surface upon which actuator 312 rolls orslides, etc. Arced track 311 could be simple a curved rail, without asupport structure (e.g., plate 310), that is, directly attached toactuator 313. Thus an “arced track” is any assembly that provides anarced trajectory to the distal end of the wafer holder having theinverted pendulum design, thus tilting the proximal end (and wafer) upona virtual pivot.

Actuator 312 moves the distal end of wafer holder 303 along arced track311. Plate 310 is immovably coupled to a second actuator 313. Actuator313 is movably coupled to a shaft 315, and moves bi-directionally alongfixed shaft 315 as indicated by the Z-axis arrows, thereby moving plate310, actuator 312, and wafer holder 303 along with it. In thisembodiment, there is component movement along the Z-axis and the X-axis,but none along the Y-axis. Thus, the assembly comprising wafer holder303, actuator 312, plate 310, and actuator 313 moves along a verticalpath (Z-axis) above the electrolyte and by this action, wafer 305 ismoved into and out of electrolyte 309.

Depicted in FIG. 3C is cross-sectional block diagram depicting a frontview of a movement scenario of an assembly 317 of wafer positioningapparatus 301 depicted in FIG. 3A and FIG. 3B. Assembly 317 compriseswafer holder 303, actuator 312, and plate 310. The distal end of waferholder 303 is movably coupled to arced track 311 via actuator 312. Forthis discussion, a point 321 on the distal end of wafer holder 303traces an arced path along 311 as the distal end is moved along arcedtrack 311 by actuator 312. As indicated by the dashed arrows, as thedistal end of the wafer holder is moved along the arced path, theproximal end of 303 is tilted from horizontal. Thus wafer 305 is tiltedon a virtual pivot 323. Pivot 323 is “virtual” in that it lacks anassociated physical pivot joint or hinge.

Referring to FIG. 3D, when point 321 is moved from its position in FIG.3C to a new position as depicted, wafer 305 (drawn with reference to itssurface 319) is tilted from horizontal upon virtual pivot 323. Describedonly for reference to movement about pivot 323, half of wafer 305 istilted 5 degrees above horizontal and half is tilted 5 degrees belowhorizontal. Thus, with respect to a plane defined by the surface of anelectrolyte in a plating bath, wafer 305 is tilted 5 degrees fromhorizontal.

FIG. 3E depicts angled immersion of the wafer 305 using apparatus 301.Apparatus 301 moves a wafer along an axis normal to the surface of anelectrolyte and tilts the wafer from horizontal, allowing for angledimmersion and angled plating. The use of a virtual pivot is oneembodiment of the tilting capability of the invention. Other embodimentsmay use actual pivot joints located in the vicinity of the wafer.Importantly, the apparatus provides two distinct movement capabilities:vertical movement along a vertical trajectory normal to the electrolyteand a tilting movement of the wafer.

The apparatus of this invention should provide wafer movement at speedsappropriate for embodiments of the invention. Preferably, rotationaldrive components of apparatus 301 can provide a wide range of rotationalspeeds for wafer holder 303. In one embodiment, it can rotate a wafer ata speed of between about 1 and 600 rpm. In one embodiment, actuator 313provides linear bi-directional movement at a speed of between 0 andabout 25 millimeters/second. Movement of the distal end of the waferholder along the arced track is provided by a hydraulic cylinder,although other suitable means can be used such as gears, lead screws,and the like. As explained, movement of the distal end of wafer holder303 along arced track 311 provides tilting of the planar plating surface319 of wafer 305 from a horizontal position, parallel to the planedefined by the surface of the electrolyte, at an angle such that theplanar plating surface of the wafer is no longer parallel to the planedefined by the surface of the electrolyte. Preferably, apparatus 301 canprovide tilt at angles of between 0 degrees and at least about 5degrees. Most preferably, the angle can be actively adjusted during anyelectroplating operation. As mentioned, the planar plating surface 319of wafer 305 is tilted at a specific swing speed, in instances when awafer need be returned to a horizontal position after immersion.Preferably, apparatus 301 can provide a swing speed of the wafer betweenabout 0.25 and 3 degrees per second. More preferably, the swing speed isbetween about 0.25 and 1.5 degrees per second. Most preferably, theswing speed is between about 0.5 and 1 degrees per second.

Although other wafer holder components can be used for the invention, agood example of a wafer holder is the clamshell apparatus as referencedabove in the background section and described in U.S. Pat. Nos.6,156,167 and 6,139,712. If a clamshell is used as the wafer holdercomponent of the apparatus, the other components essentially comprisepositioning elements for the clamshell, since the clamshell hasnecessary electrical contacts, holding and rotational components, etc.

FIG. 4A provides a perspective view of an improved clamshell apparatusfor electrochemically treating semiconductor wafers. The actualclamshell comprises a cup 402, which holds a wafer, and a cone 403,which clamps the wafer securely in cup 402. Cup 402 is supported bystruts 404, which are connected to a top plate 405. This assembly(402-405) is driven by a motor 407, via a spindle 406. Motor 407 isattached to a mounting bracket 409. For the purposes of this discussion,the assembly comprising components 402-409 is referred to as a waferholder 411. Note however, that the concept of a “wafer holder” extendsto various combinations of components that engage a wafer and allow itsmovement and positioning.

In this example, wafer holder 411 has a proximal end (nearest cup 402and cone 403) and a distal end (nearest mounting bracket 409).Conventionally, mounting bracket 409 is used to mount wafer holder 411to an actuator that moves the entire assembly vertically up and down toimmerse the clamshell (proximal end) into a plating bath.

In accordance with this invention, mounting bracket 409 as depicted isfastened to a first plate 415 that is slidably connected to a secondplate 417. A drive cylinder 413 is connected both to plate 415 and plate417 at pivot joints 419 and 421, respectively. Thus, drive cylinder 413(a first actuator) provides the force for sliding plate 415 (and thuswafer holder 411) across plate 417.

FIG. 4B provides a perspective view of assembly 423, comprising mountingbracket 409, plate 415, drive cylinder 413, and plate 417. Plate 415contains a channel 425. Referring now to FIG. 4C, presenting a differentperspective view of assembly 423, plate 417 can be more clearly seen.Plate 417 has integral to it an arced track 427, which fits withinchannel 425 of plate 415. Thus when drive cylinder 413 is actuated,plate 415 (and wafer holder 411 not shown) slides across plate 417 in anarced path. This provides the angle adjustment for the wafer holder. Thedistal end of wafer holder 411 (i.e. mounting bracket 409) is movedalong an arced path, and thus the proximal end of wafer holder 411 (i.e.the clamshell holding the wafer) is tilted upon a virtual pivot. Thisassembly can be described as an inverted pendulum.

By analogy to FIGS. 3A-3D, drive cylinder 413 is a first actuator andplates 415 and 417 provide the arced track and coupling of wafer holder411 to this drive mechanism. As mentioned, mounting bracket 409 is usedconventionally to mount wafer holder 411 to an actuator that moves theentire assembly vertically up and down to immerse the clamshell(proximal end) into a plating bath. In this invention, plate 417 is usedto mount wafer holder 411 to said actuator (a second actuator) thatmoves the entire assembly vertically up and down to immerse theclamshell (proximal end) into a plating bath. Thus, a two-componentpositioning apparatus provides both vertical movement along the Z-axisand a tilting movement along the X and Z-axes. Many existing clamshellelectroplating apparatus do not have this capability. Because of thedesign of assembly 423, it can be provided as a retrofit for existingsystems.

Embodiments of the present invention may employ various processesinvolving data stored in or transferred through one or more computersystems. Embodiments of the present invention also relate to theapparatus, such computers and microcontrollers, for performing theseoperations. These apparatus and processes may be employed to control thewafer positioning parameters of methods of the invention and apparatusdesigned to implement them. The control apparatus of this invention maybe specially constructed for the required purposes, or it may be ageneral-purpose computer selectively activated or reconfigured by acomputer program and/or data structure stored in the computer. Theprocesses presented herein are not inherently related to any particularcomputer or other apparatus. In particular, various general-purposemachines may be used with programs written in accordance with theteachings herein, or it may be more convenient to construct a morespecialized apparatus to perform and/or control the required methodsteps.

While this invention has been described in terms of a few preferredembodiments, it should not be limited to the specifics presented above.Many variations on the above-described preferred embodiments may beemployed. Therefore, the invention should be broadly interpreted withreference to the following claims.

What is claimed is:
 1. A method of immersing a wafer into an electrolyteof an electroplating cell, the method comprising: (a) positioning thewafer above the electrolyte surface while holding the wafer in a waferholder having a proximal end that engages the wafer; (b) directing adistal end of the wafer holder along an arced track, thereby pivotingthe wafer about a pivot point, without substantially translating thewafer, to tilt the wafer at an angle such that the planar platingsurface of the wafer is not substantially parallel to the plane definedby the surface of the electrolyte; (c) moving the wafer toward theelectrolyte along a trajectory substantially normal to the plane definedby the surface of the electrolyte; and (d) immersing the wafer into theelectrolyte while the wafer is tilted.
 2. The method of claim 1, whereinthe wafer is rotating about an axis normal to the plating surface of thewafer during immersion into the electrolyte.
 3. The method of claim 2,wherein the angle of the wafer's planar plating surface with respect tothe plane defined by the surface of the electrolyte is adjusted betweenabout 1 and 5 degrees.
 4. The method of claim 2, wherein the waferrotates at a speed of between about 1 and 150 rpm.
 5. The method ofclaim 4, wherein the wafer rotates at a speed between about 100 and 150rpm, and wherein the wafer is about 200 millimeters in diameter.
 6. Themethod of claim 4, wherein the wafer rotates at a speed between about 50and 100 rpm, and wherein the wafer is about 300 millimeters in diameter.7. The method of claim 6, wherein the wafer rotates at a speed of about70 rpm.
 8. The method of claim 1, further comprising adjusting the angleof the wafer's planar plating surface with respect to the plane definedby the surface of the electrolyte while the wafer is stationary withrespect to a direction normal to the plane defined by the surface of theelectrolyte or while the wafer is moving toward the electrolyte alongthe trajectory substantially normal to the plane defined by the surfaceof the electrolyte.
 9. The method of claim 1, wherein the tilting in (b)is performed while the wafer is stationary with respect to the directionnormal to the plane defined by the surface of the electrolyte.
 10. Themethod of claim 1, wherein the angle of the wafer's planar platingsurface with respect to the plane defined by the surface of theelectrolyte is about 5 degrees or less.
 11. The method of claim 10,wherein the angle of the wafer's planar plating surface with respect tothe plane defined by the surface of the electrolyte is between about 4and 5 degrees.
 12. The method of claim 1, wherein moving the wafertoward the electrolyte occurs at a speed between about 5 and 50millimeters/second.
 13. The method of claim 12, wherein moving the wafertoward the electrolyte occurs at a speed between about 5 and 25millimeters/second.
 14. The method of claim 12, wherein moving the wafertoward the electrolyte occurs at a speed between about 8 and 15millimeters/second.
 15. The method of claim 14, wherein moving the wafertoward the electrolyte occurs at a speed of about 12 millimeters/second.16. The method of claim 1, wherein the (a), (c), (b), and (d) areperformed in that order.